1) Field of the Invention
The present invention relates generally to implements such as disk harrows, and more specifically to an improved cushion standard for such implements.
2) Related Art:
Disk harrows include gangs of disk blades supported for rotation by bearings mounted on bearing hangers or standards which extend downwardly from the frame of the disk. Severe loads encountered in rough and rocky soil conditions often cause premature failure of disk blades, blade spacer spools, gang bolts and bearings. To reduce breakage, various types of cushioning devices have been made available which permit disk gang movement relative to the frame. A typical cushioning device such as a C-spring bearing hanger facilitates both vertical and some transverse gang movement for movement over and around obstacles such as rocks. Although the C-spring hangers afford some measure of gang protection, abbreviated fatigue life and limited flexibility of such hangers have heretofore continued to be problematic. Increasing the cross-section of the C-spring increases the fatigue life of the spring but results in a stiffer spring which transfers more destructive loading to the disk gang assembly. Some disk harrows are fitted with mechanical stops, or with helper springs such as shown in U.S. Pat. No. 4,407,372, to improve C-spring life, but these devices also cause more damaging loads to be transferred to the disk gang assembly. Other types of cushioning arrangements, such as the spring device illustrated in U.S. Pat. No. 4,333,535 reliably prevent disk gang assembly damage but have the disadvantage of being expensive to manufacture and assemble.
Various attempts have been made in the past to fabricate C-springs with non-uniform or tapered cross-sections to improve flexibility while maintaining good fatigue life. However, previously available tapered C-springs have experienced a less than desirable combination of flexibility and service life, particularly in rocky conditions present in many locations where the use of disk harrows is popular. Reasons for the lack of success of the tapered C-springs apparently include the lack of understanding of the stress distribution and failure pattern in the springs and the use of tapered sections that were originally designed for chisel plow shanks wherein the start of the taper is located at or near the start of the top bend radius on the upper portion of the C-spring. Previously, stress was measured on the outside of the radius of the C-spring, and it was assumed that the middle or forwardmost nose of the C-spring received the highest stresses. A uniform stress distribution along the entire C-spring was generally not achieved, and early breakage due to fatigue in the upper forward quadrant of the C-spring was common.